This is the first of four articles where you can decide on the best strategy when presented with different binocular vision challenges

Do you accept the challenge to help you deepen your knowledge on binocular vision? Do you have the skills and courage to solve your patient’s problems and create a loyal patient for life…take the test now!

Your Challenge

A 30-year-old female banker presents for an eye examination. She has been experiencing trouble with reading her paperwork and her computer at work for the past two months. She returned to work after six months’ maternity leave. She reports that by mid-morning print becomes blurred and she has to blink to clear it. By lunch time she is aware of ‘eye strain.’ She also reports she experiences dull frontal headaches towards the end of the day around three to four times a week.

Her distance vision is good and she does not wear spectacles. Other than the reported symptoms, her general health is good apart from tiredness due to her sleep being disrupted by the baby. She is not on any medication. Ocular and family history are unremarkable. Go to walkthrough.

Walkthrough

For each step of the process, decide on the option you wish to take. Then go to the step indicated. When you make the correct choice, you will be helped towards the next step. Once you have completed the challenge it should become clear which is the most systematic approach to investigate the asthenope.

STEP 1 You look in your equipment bag and see a retinoscope and an occluder. Do you decide to do a refraction go to 2 ? or a cover test go to 3 ??

STEP 2 You do retinoscopy and your subjective refraction is;

R; (6/5) +.025/-0.25 x 10 (6/5 and N5)

L; (6/5) plano (6/5 and N5)

Bin; 6/5 and N5.

You have gained an ophthalmoscope and an RAF ruler (Figure 1).

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Which test would you do next?

Ophthalmoscopy – go to 4 ?

Amplitudes of accommodation – go to 5 ?

STEP 3 Without vision or visual acuity this would be inaccurate. Go to 2 ?

STEP 4 The fundus looks healthy. Ophthalmoscopy is appropriate in all cases, although at this stage of the investigation it would probably not help you diagnose her symptoms. Go to 5

STEP 5 You carefully place the RAF ruler on her cheeks to do the measurement. The amplitude of accommodation is 8.00D R and L, binocularly 8.50D. You remember that this is normal for her age range and do not need to consider a cycloplegic refraction.

You decide on the next step. Which will it be?

Cover test - go to 6 ?

Motility - go to 7 ?

STEP 6 You perform an accurate cover test using a target 2 lines above their best corrected VA and find the results to be:

Distance: moderate exophoria, good recovery

Near: moderate exophoria, good recovery

You ponder the results and spot a pen torch on your table and a Mallet Unit (Figure 2).

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What do you do next?

Motility - go to 7 ?

Check fixation disparity - go to 8 ?

STEP 7 Ocular eye movements look normal. You decide to pick up the Mallett unit and check for fixation disparity - go to 8 ?

STEP 8 You check for aligning prism and find distance and near to be R 1? base in and L 1? base in. You rack your brains to remember what this means.

Either;

It agrees with the heterophoria results gained on cover test

It disagrees with the heterophoria results gained on cover test

Which is it?

Agrees – continue

Disagrees – start 8 again ?

You want to consider more compensation tests for near.

You now have access to a Maddox Wing and a Titmus fly test (Figure 3)

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You need to decide on your next measurement;

Near point of convergence - go to 9 ?

Stereopsis - go to 10 ?

Maddox Wing - go to 11 ?

STEP 9 You measure the near point of convergence which appears normal at 10cm. The patient starts to look at their watch. It is time to start thinking about wrapping up the consultation… from your results you have to prepare your advice to the patient. You clear your throat and announce to the patient they have;

a) presbyopia - go to 12 ?

b) decompensating heterophoria - go to 13 ?

c) suspect eye disease - go to 14 ?

STEP 10 You use a Titmus fly test and find that the patient achieves 100’ which seems normal but you remember that you should check convergence. Go to 9 ?

STEP 11 The Maddox Wing looks dusty; it looks like it has not been used for a long time. You give it a quick clean before handing it to the patient. Her measurements are 12 ? exophoria, no hyperphoria. You wonder how useful that was. You decide to do stereopsis . Go to 10 ?

STEP 12 The patient gets angry that you suggest she is ‘old’ and her focusing is receding. You quickly reconsider your options. Go to 13 ?

STEP 13 You explain that she has a mild muscle imbalance which seems to be breaking down and causing her symptoms. This is probably due to her recent change in environment and having to use her eyes for a lot more screen work. The patient nods in agreement.

Your management is one of the following:

a) prescribe the low correction found to help with screen work - go to 15 ?

b) prescribe 1? base in right and left for screen work - go to16 ?

c) give convergence exercises to improve relative positive fusional reserves - go to 17 ?

d) give advice about visual hygiene, such as taking regular breaks and ensuring there is no discomfort glare off the VDU screen - go to18 ?

STEP 14 The patient looks worried. You decide to examine her ocular health including fields and tonometry, all which appears normal. You breathe a sigh of relief and reconsider your options. Go to 9 ?

STEP 15 The patient purchases these and comes in 2 weeks later. They have made no difference. Go to back to 9 ?

STEP 16 The patient purchases the glasses with prisms. You ring her after a week to check on her progress. She has found them useful in relieving her symptoms. You advise her to take regular breaks too. The patient is happy and recommends all her family to your practice. Well done! Go to summary section on page 20.

STEP 17 The patient returns after 2 weeks. Her symptoms remain and she has to admit she has little time to do the exercises. You consider alternative management. Go to back to 13 ?

STEP 18 You ring the patient after 1 week. She is fairly happy most days as her symptoms have reduced. But on some days when the workload is heavy she is still not symptom free. You consider the option of prescribing prisms for her. Go to 16 ?

Summary of the case – You have completed this level

There are two ways a practitioner can address any patient’s symptoms and reach a diagnosis and it may be useful to identify which camp you belong to. This applies to any ocular condition but especially useful when you suspect a binocular vision anomaly. You may find that, for familiar conditions, you would follow the second method, and in cases where you are not sure you would follow the first route.

  • The Rigid Routine: The first method is use all the battery of tests available to you and look at all the results. This is what the above ‘fighting fantasy’ adventure employs. From these, hopefully, a pattern will emerge and you may then identify the condition that explains these features. This method is very useful if you are unsure where to start. As you do your ‘routine’ of tests, clues to a likely diagnosis appear, and this leads on to more specific tests to confirm the diagnosis. You may do more tests than necessary, but occasionally you may get an anomaly that could lead you to a different diagnosis were you not to have done so. An example would be when convinced a patient has a contact lens related problem when complaining of reduced visual acuity with their lenses and actually, by investigating ophthalmoscopy or refraction, an alternative diagnosis is found. The disadvantage is clearly that having lots of investigations can be time consuming (and boring for the patient), some of which may be unnecessary.

  • The Funnel Routine: Experienced practitioners may identify the differential diagnosis from the symptoms presented. They should then perform the appropriate tests that confirm this. In other words, you have the end result in mind and you are ruling out other conditions as you go along. The advantage of this method is it is quicker to reach the diagnosis as only the tests that you think are ‘relevant’ are done. This method is also particularly useful for ocular emergencies, such as with a painful red eye. The disadvantage is that you may become fixated on a diagnosis and miss other vital clues.

First principles

It is also helpful to know the simple rules of binocular vision; in order to experience comfortable binocular single vision, there must be:

  • Two healthy eyes with clear vision (binocular vision)

  • A muscle system with correct signals to keep images on the foveas during eye movements (motor fusion)

    The ability to perceive two images as one, at the level of the brain (sensory fusion)

For the discussion, we will look at the differential diagnoses:

Uncorrected refractive error

Uncorrected hypermetropia can cause asthenopia symptoms as the patient is having to accommodate excessively to compensate for refractive error and close work. Significant astigmatism would give blurred vision or fluctuations in accommodation. Myopia is unlikely in this case as distance vision is clear and even if mild amounts of myopia aid near vision as less accommodation is required.

The exception could be in a pre-presbyopic patient with exophoria, where less accommodation and hence accommodative convergence would result in less control of the deviation. Anisometropia may also need correcting as one eye may be ‘working harder’ depending upon the prescription.

In summary, the cause of the symptoms may be due to blurred vision or excessive accommodation required, leading to a challenge to compensate for a phoria or tropia.

Tests required:

  • Refraction. Include retinoscopy to help detect fluctuations in reflex and consider cycloplegia if necessary.

Management: Correct significant hypermetropia, astigmatism, and anisometropia. In this case, the refraction was insignificant and unlikely to cause the symptoms. To see the effect of the refraction on ocular motor balance, always check cover test and fixation disparity before and after refraction, as this may influence your final prescription.

Ocular motor balance – decompensated heterophoria or heterotropia

A breakdown in a previously compensated heterophoria or heterotropia could produce symptoms described. This applies to the motor element of first principles.

Tests required:

  • Cover test – to identify any heterophoria or tropia.

  • Compensation tests – fast cover test recovery movement; little or no aligning prism for distance and near fixation disparity;

  • Stereopsis – stereoacuity helps to give an idea of the stability of the binocular vision. The use of Maddox rod or wing, which has its uses in identifying the magnitude of the phoria or tropia has not been found to be the most predictive of symptoms. Large phorias can be asymptomatic. Also it can overestimate the magnitude of deviations, much like prolonged repeated cover testing. It has some uses for monitoring the size of the deviation over time and is easy to understand and use.

  • Motility – check for comitancy and incomitancy where the angle of deviation varies in different directions of gaze. You must exclude pathology for all recent onset incomitancy.

Management: This patient has an exophoria which could be breaking down as she is working at the computer. She has aligning prism which suggests her motor system is struggling to control her phoria. The cause of decompensation would then need to be identified and removed. It would seem likely the return to work after a break would put a strain on her visual system. Discussing regular breaks and identifying any other environmental factors such as glare or poor lighting would help. The combination of sleep deprivation and fatigue would also contribute to this, although difficult to address until the baby’s sleep patterns stabilise. Orthoptic exercises can improve positive fusional reserves, and this would help with compensating exophoric conditions. This patient is possibly likely to be too busy and less motivated to undertake exercises adequately due to her lifestyle, so prisms may be a good option as a temporary measure.

A spherical correction may also be appropriate in those with adequate amplitudes of accommodation. The amount can be established by using small positive power lenses to control eso (convergent) deviations while using the near Mallett Unit to monitor any slip and vice versa for exo slip. In all cases, the best outcome is the one agreed by both practitioner and patient. The patient given the option of prism, exercises and advice can make an informed choice about what would suit her best. This is more likely to lead to success in the treatment of her decompensating heterophoria.

Disease

The possibility of disease should always be excluded, especially where symptoms do not improve after any initial intervention. In this case, as the symptoms appear to be triggered by visual use, it would seem unlikely that pathology is involved. With reference to first principles, a clear image is required and so clear media in the ocular structures would benefit binocular vision. Any trauma or disease affecting the extraocular muscles would affect the motor element of binocular vision and result in potential symptoms.

Tests required:

With all headache, it is useful to have some baseline neurological tests including;

  • Pupil reactions

  • Monocular colour vision

  • Visual fields assessment

As with all eye examinations, one would check ocular health with slit lamp and ophthalmoscopy (in particular, indirect to look for swollen discs) and, if available, fundus photography. Gathering information about general health eg. thyroid disease, diabetes, hypertension, strokes would alert you to the potential cause of recent onset binocular symptoms.

Management: Referral for all ocular pathology found and any suspected systemic diseases to be investigated by the GP.

Convergence and accommodative issues

For symptoms associated with close work these are important areas to investigate. In this case, there were no significant findings.

Tests required:

  • Near point of convergence – if reduced, this would indicate convergence insufficiency, a common cause of similar symptoms and easily managed

  • Amplitudes of accommodation – measurements would give clues indicating latent hypermetropia or accommodative spasm

Management: Treat convergence insufficiency with exercises or, in some cases, base in prisms. Exercises should always be followed up at short intervals, ideally two to four weeks to ensure compliance, motivation and success. It is the same principal as if your gym trainer only saw you once every six months, the likelihood of your fitness improving is slim! Accommodative anomalies may benefit from prescribing a near addition or recommending orthoptic exercises (eg. ‘accommodative rock.’) If you do not have the time or inclination to monitor these, it may be in the best interests of the patient to be referred to another specialist practitioner or orthoptist

Environment, activities and well-being

Environmental factors that can affect binocularity include the room environment, lighting and workstation layout. The room temperature, heating or air conditioning can affect the tears and comfort of the patient. Poor lighting or disability glare would reduce visual acuity and hence binocularity. The activities undertaken can also lead to a strain on the binocular system, especially in a change of use of the eyes commonly during revision for exams or new job roles. This patient had returned to work so there was a significant increase in her close digital screen workload. Her general health was good, but a lack of sleep could also reduce her ability to compensate for her heterophoria. Ill health is a common reason for causing binocularity breakdown and, in cases where these are long standing, the use of corrective prescription or prisms are often more appropriate than orthoptics.

Tests required:

  • Thorough symptoms and history and visual task analysis

Management: Taking regular breaks, removing sources of glare, improving work station layout and any other source of disruption.

Summary

Investigation of asthenopia will involve evaluating the binocular function of the patient. By experience practitioners can use readily available tests found in practice consulting rooms. The management may include advice, refractive error correction, prisms, orthoptic exercises or onward referral.

Sosena T.W. Tang practises at Aves Optometrists in Ware, Hertfordshire and QEII Hospital, East and North Herts NHS Trust. She is a College of Optometrists Assessor